Vibrating ball mill method and apparatus



Nov. 2, 1965 E. w. SMITH 3,215,354

VIBRATING BALL MILL METHOD AND APPARATUS Filed Nov. '7. 1961 L 2 Sheets-Sheet l Nov. 2, 1965 E. w. SMITH VIBRATING BALL MILL METHOD AND APPARATUS 2 Sheets-Sheet 2 Filed NOV. 7, 1961 3 INVENTOR.

BY EDWARD w. SMiTH WWW.

United States Patent (3 3,215,354 VIBRATWG BALL MILL METHQD AND APPARATUS Edward W. Smith, 47 Lovell Road, Melrose Highlands, Mass. Filed Nov. 7, 1961, Ser. No. 150,704 16 Claims. (Cl. 24130) The present invention relates to a ball mill and to a method for continuous wet milling. More particularly the present invention relates to a means and method for Wet milling in which a solid material is to be dispersed in a liquid phase, as for example in the grinding of paint.

It has been common in Wet milling to put solid material and liquid in a large drum together with steel or ceramic balls or other grinding particles such as Danish pebbles. The drum is rotated at a speed which is dependent upon its diameter so that the grinding particles will be raised through centrifugal force to the periphery of the rotating drum from which the grinding particles will fall through the diameter of the drum onto the solid material below. The successive impacts of the particles on the solid mamaterial below. The successive impacts of the particles on the solid material below comminutes the material in the liquid.

This means and method are effective if the material is ground for long periods of time, such as 25 to 30 hours. Such processing is limited both because of grinding time required and because it is a batch process. Faster results may be obtained if the density of the grinding particles is increased, other parameters being equal. Increasing the speed of rotation, however, is limited by the density of the grinding particles. Quite often metal balls are not suitable because they may contaminate the material being milled. Ball mill drums have also been vibrated longitudmally in addition to rotating them in order to increase the acceleration of the particles. Such devices reduce normal grinding time but not sufiiciently for commercial continuous wet grinding. Continuous dry grinding has been accomplished on a limited basis in such structures by continuously removing fines by a current of air passing through a conventional ball mill while rotated. Larger particles are left in the mill for further treatment. This procedure however is not satisfactory for wet grinding for various reasons and particularly because of the large amounts of liquid which would be required.

It is an object of the present invention to provide a means and method whereby accelerations many times that of gravity and in the order of 65 to 70G may be delivered to grinding particles in a ball mill system. Another object of the present invention is to provide a ball mill having a resonant actuating system with sufiicient stiffness in the system for imparting accelerations up to 65 to 70G, to the masses referred to with the components providing the stiffness having negligible weight. A further object of the present invention is to provide means whereby the material to be comminuted into liquid may be subject to the action of vibrating particles, accelerated with forces in excess of 65 to 70G. A further object of the present invention is to provide an improved means and method for comminuting material at a rate more rapid heretofore possible.

It is also an object of the present invention to provide a means for milling material on a continuous basis at rates faster than heretofore possible. One further object of the present invention is to provide a means which may be used for either batch milling or continuous milling of material.

The present invention provides an improved method and means for accelerating grinding particles to rates of acceleration substantially in excess of the earths gravita- 'ice tional pull and normally in the neighborhood of to 706 substantially regardless of the particle density. The mill is formed as a mechanically resonant system having a container for grinding particles and the material to be ground.

This container forms a first mass which is connected toone end of a spring means. The other end of the spring means is rigidly secured to a second mass capable of exerting a force which is always equal and opposite to the force exerted when the spring means is periodically compressed and extended. Means are provided for setting these two masses and interconnecting spring means in resonant vibration at a rate of acceleration substantially in excess of the acceleration of gravity. The second mass referred to may comprise a second container constructed similarly to the container forming the first mass or alternately may comprise a mass of substantially greater weight than the weight of the first mass. Where the first and second masses are equal in weight, the two masses will move apart and come together periodically and in synchronism.

These and other objects of the present invention will be more clearly understood when considered in conjunction with the accompaniying drawings in which:

FIG. 1 is a schematic illustration of the principal upon which the present invention is based;

FIG. 2 is a cross sectional elevation showing in somewhat schematic form a preferred embodiment of the present invention;

FIG. 3 is a cross section of FIG. 1 taken along the line 33 of FIG. 1; and

FIG. 4 is a cross section taken substantially along the line 4-4 of FIG. 2.

The principle upon which the present invention is based involves the use of a special form of mechanical resonance to achieve high frequency vibrations of the masses involved and may be called a two-mass resonance system. Ordinarily a mechanically resonant system in the simplest form consists of a spring S connected to a weight W, the other end of the spring being solidly secured to some rigid substantially immovable object as at a point P as shown in FIG. 1. If the weight W which we can assume for the moment as being supported on a frictionless surface is displaced along its axis and then released, it will vibrate at a frequency determined by the size of the weight and the stiffness of the spring. The kinetic energy of the moving mass is transferred periodically into potential energy in the compressed or elongated spring and vice versa.

While this arrangement is adequate in a vibratory system for small weights and low frequencies of vibration, it is unsatisfactory for large weights and high frequencies because it presupposes that the end of the spring is solidly secured to a mass which is large compared to W. The problem is solved in the present invention by providing a force at the point P which is always equal and opposite to the force exerted by the periodical compressions and expansions of the spring S. Thus, by setting another weight vibrating in a similar manner but in an opposite direction at the same frequency and attached to the spring at point P, we have in effect a mirror image of the vibrating weight W as illustrated by the broken lines in FIG. 1. The forces therefore exerted at point P are always equal and opposite to each other so that we have in effect obtained a large mass such as referred to above without having had to actually build it. Under these conditions the weights W and W fly apart and come together periodically and in synchronism.

An embodiment of the invention utilizing these principles is illustrated in FIG 2. In this arrangement the system comprises a container means 10 forming a first mass, a spring means 11 interconnected at one end 12 to the first mass and at the other end 13 to a second mass 14. Electromagnetic means 15 are provided for establishing the first and second masses in resonant vibration in a manner more clearly described hereafter. The entire structure is suitably supported on a frame 8 to permit longitudinal oscillation of the masses 10 and 14.

The container means 10 comprises a plurality of elongated passages 16 arranged in rows and columns illustrated in FIG. 3 by the arrows 17 and 18 respectively. These passages may be formed of suitable tubes of metal supported in a frame as illustrated at 19. Plates 20 and 21 cover the opposite ends of these passages 16 and are formed with connecting passages, 22, 23 which interconnect adjacent passages 16 in such a manner that adjacent passages 16 in each column 18 are connected in series, the end passages 16 in each adjacent row 17 are also connected in series and the outermost ends of the series connected tubes are open as illustrated at 25 and 26. The plates 20 and 21 may be removably secured to the frame by means of nuts and bolts 27, 28 which secure the plates to the frame 19. The ends of the passages 16 are covered by a screen 30, 31 of sufiiciently small mesh to retain grinding materials such as steel balls or Danish pebbles within the passages 16 but with the meshes sufficiently large to permit passage of the material being processed through the series connected passages 16. This material is carried in a liquid phase, under normal conditions with the rate of flow of material through these passages governed by the speed with which the liquid carrier is forced into the opening 25. If the tubes 16 are each 12" long as illustrated in FIG. 1 and there are 144 tubes, the mixture has to be passed through 144 feet of tubing 16 at a rate governed by the flow of fluid. During this time the material is subject to the action of the grinding material each time it passes through one of the tubes 16.

In the embodiment illustrated the removable plates 20 and 21 facilitate cleaning of the tubes which is quite important in many types of ball milling. In addition the plates 20, 21 having passages 22, 23, may be replaced with fiat plates without passages so that the ends of the tubes 16 are effectively sealed from one another thereby forming the tubes or passages 16 into a plurality of individual containers which may be used for batch ball milling if desired.

If the construction is not designed to be used for both continuous and batch grinding, the plates 20, 21 may be welded to the ends of the tubes 16 to provide a more permanent arrangement. In this and the preferred construction of the tubes 16 may be surrounded by heating or cooling means for grinding at controlled temperature levels. The heating coils may be wrapped around the tubes 16 or a cooling water jacket may be provided for the container means 10. Ball milling under controlled temperature conditions is particularly useful in the manufacture oi virious products including for example certain types 1n The container means is supported for longitudinal movement by frame 8 in the direction of arrows A and is interconnected to spring means 11 by a shaft 35 connected at one end 36 to the center of the frame 19 supporting the container means 10. The other end 37 of the shaft is connected to a second frame 38 having outwardly extending flange members 39 secured at their outer ends 40 to one half of each of the electromagnetic means 15. A collar 41 is integrally formed on one surface 42 of the frame and is threadingly interengaged with the spring means at 44. The spring means 11 comprises a plurality of fiat members 50, 51, arranged parallel to one another and in pairs. Each fiat member is preferably formed as a disc having inwardly extending lips 53 on the inner surface with the lips 53 of each pair 50, 51 matching each other in face to face relation and thereby spacing the two members apart, forming a bellow-like gap 55 intermediate the members 50, 51. The peripheries of the members 50, 51 are rigidly and solidly interconnected by a series of nuts and bolts 59, 60 about their entire peripheries. The outer surfaces of each flat member is provided with a projection 61 extending from the center of the member and preferably having its outer surface threaded as illustrated at 63. Adjacent pairs of members 50, 51 are interconnected by sleeves 64 internally threaded and partially engaging each of aligned and adjacent projections 61. The projections 61 at the one end of spring means 11 is threaded into the collar 41 while the projection 61 at the other end of the spring means is aligned with an externally threaded projection 66 and is interengaged with it by an internally threaded sleeve 67. Projection 66 is integral with the second mass 14.

The second mass 14 may comprise a substantial weight or a weight having substantially the same weight as the mass of container 10. Alternately the second mass 14 may comprise a mirror image of container means 10, and thus may provide a dual resonant system in which continuous ball milling is conducted in two container means simultaneously.

The electromagnetic means for establishing a resonant vibration in the first and second masses 10, 14 and spring means 11 comprise preferably four electromagnets illustrated at 71, 72, 73 and 74. Each electromagnet comprises a pair of symmetrically arranged armatures 78a and 78b and stators 77a and 77b. The stators are each E-shaped and have a coil 79 wrapped about their center leg 80. These stators are coplanarly arranged with their center leg 80. These stators are coplanarly arranged with their legs facing one another and are supported in a yoke 82 having legs 83, and 84 with inner surfaces inclined at an acute angle to each other. The yoke 82 is in turn supported on a base 89 which is rigidly secured at its other end 90 to the second mass 14. The armatures 78a and 78b are formed of fiat plates positioned in spaced relation to the ends of the legs of the E-shaped stators forming a gas therebetween. One surface 85 of each armature is suitably and rigidly secured to an arm 86 which is connected at its other end 87 to the outer end 40 of the second frame 38 as previously described.

In designing the system described, care must be taken to adjust the mass of the container means 10, the second mass 14 and the stiffness of the spring means 11 in relation to one another. These components are interrelated by the formula M! J!!! M 34" where W=21rf,

M=mass in grams to be vibrated, M"=the mass of the counter balance in grams, and u is the stiffness in dynes/crn.

Substituting the values set forth above, we have =9.7(10) dynes/cm =20,800 lbs./%

The stiffness of the circular or disc-like members 50, 51 forming the spring means when clamped at its edges and loaded at its center is determined by the formula where E equals Youngs modulus in dynes/cm. t is the diaphragm thickness in cms., and R is the eflective radius in cms.

If the diaphragm is made of steel and therefore has a Youngs modulus of 30,000,000 lbs/sq. inch, converted to the metric system we have E=2.07() dynes/cm? If the member has an effective diaphragm diameter of 12" and therefore a radius of 6" (15.25 cm.) and is A" thick (.635 cm.), we may substitute in the above equation as follows:

In the foregoing example where 300 lbs. of material and container are to be vibrated a stiffness of the square root of 12 x 9.7(10) dynes/cm. was required. It is therefore obvious that by slight adjustment either the diaphragm thickness or diameter required stiffness can be obtained. Since it is preferable to keep down fiber stress in diaphragms of the type described it should be allowed to deflect no more than Thus if 12 diaphragms were stacked together, the edges of each pair of diaphragms clamped together and the centers of each pair clamped to the next pair as illustrated in the disclosed embodiment, a stack of such diaphragms or members may be built up to provide the required deflection. In the present case as illustrated six pairs of two diaphragms each having a deflection of no more than would permit a total deflection of approximately Referring to the electromagnetic means 15, suitable connections are made to the coils 79 to provide periodic energization at the resonant frequency vibration of the system. If the coils 79 are energized at this frequency, a minimum amount of power is required, for the energy required is only that necessary to replace the energy for work actually done plus a small amount of frictional loss and the like. In this connection the stator and armature elements should be placed at an angle such as illustrated with respect to the axis of the unit. This arrangement permits the passages or tubes 16 to vibrate through relatively large distances, in the case of the example without duly increasing the separation between stator and armature element. By minimizing the maximum amount of gas between the stator and armature, the power re quired may be minimized.

What is claimed is:

1. A method of continuously grinding material comprising, feeding material continuously in a path having parallel segments in series, said parallel segments being stationary with respect to one another, confining grinding particles in said parallel segments, and vibrating said material and particles while in said segments of said paths and in a straight line direction normal to the axis of said segments and with a force substantially in excess of the force of gravity.

2. A method as set forth in claim 1 wherein said force substantially in excess of the force of gravity is in the order of at least 65G.

3. A system for continuous grinding of material comprising means having a first mass for containing said material and grinding particles, a spring means connected at one end to said rnass, said spring means comprising a plurality of parallel spaced flat members arranged in pairs, means rigidly securing the peripheries only of the members of each pair together and with adjacent members of diflerent pairs interengaged at their centers only, a second mass restraining the other end of said spring means from movement, said spring means and masses comprising a resonant system wherein the resonant frequency, the stiffness of said spring, the value of said masses and the weight of said material and particles are interrelated by where f the resonant frequency of the system,

u=the stiffness of the spring means in dynes/cm.,

M'=the total mass in grams to be vibrated including said first mass and said material and particles contained therein, and

M"=said second mass,

and means for establishing and maintaining said resonant system in resonance whereby said first mass is resonantly vibrated for agitating said material and particles contained therein.

4. A system for continuous grinding of material comprising means having a first mass for containing said material and grin-ding particles, a second mass substantially equal to said first mass, spring means interconnecting said masses to form a resonant system according to the formula MI MI! whw where f=the resonant frequency of the system,

u=the stiffness of the spring means in dynes/cm.,

M'=the total mass in grams to be vibrated including said first mass and said material and particles contained therein, and

M"=said second mass,

said spring means comprising a plurality of parallel spaced flat members arranged in pairs, means rigidly securing the peripheries only of the members of each pair together and with adjacent members of different pairs interengaged at their centers only, and means for establishing and maintaining said resonant system in resonance whereby said first mass is resonantly vibrated for agitating said material and particles contained therein.

-5. A system for continuous grinding of material comprising, means having a mass for containing said material comprising a plurality of elongated containers positioned with their longitudinal axes parallel to one another, means interconnecting said containers end to end in series whereby said material may be fed consecutively through said containers, means for vibrating said mass in and means for limiting movement of said mass to a straight line direction normal to said axis with a rate of acceleration in excess of the acceleration of gravity.

6. A system as set forth in claim 5 wherein said means interconnecting said containers each comprise a means forming a passage interconnecting the ends of containers, and a screen positioned at each end of said containers and adapted to confine grinding material within said container while at the same time allowing the passage therethrough of said material.

7. A system as set forth in claim 5 wherein said plurality of elongated containers are positioned in parallel rows and columns, said means interconecting said containers comprising end plates having passages formed therein with said passages interconnecting the ends of said containers, screens positioned at each end of said containers and adapted to confine grinding material within said container while at the same time allowing the passage therethrough of said material.

8. A system for continuous grinding of material comprising, means having a first mass for containing said material, a second mass, spring means interconnecting said masses, said spring means comprising a plurality of parallel spaced fiat members, arranged in pairs, means securing said members of each pair together at their periphery only, and means interengaging adjacent members of different pairs together at their centers only, and means for establishing said masses and spring means as .a resonant system with said first mass vibrating at the resonant frequency of said system and at a rate of acceleration substantially in excess of the rate of acceleration of gravity.

9. A system as set forth in claim 8 wherein said flat members each comprise circular discs with a projection from the center of each disc projecting outwardly therefrom towards the next adjacent pair of members, with said means interengaging adjacent members comprising sleeve means interconnecting projections of adjacent means.

10. A system as set forth in claim 8 wherein the still?- ness of said members when loaded at the center and clamped at the edges are each determined by the formula where E=Youngs modulus in dynes/cmx' t=the thickness of the member in cms., and R=the elte ctive radius of the members.

11. A system as set forth in claim 8 wherein the outermost of said members are connected one to said first mass and the other to said second mass.

12. A system as set forth in claim 8 wherein said means for establishing said masses and spring means as a resonant system comprises electromagnetic means having an armature and stator with said armature connected to one mass and the stator to the other and forming a gap therebetween such that when said stator is energized and deenergized at said resonant frequency said masses will move toward and away from one another at said resonant frequency.

1 3. A system as set forth in claim 12 wherein said stator is E-shaped with the coil thereof wound about the center 'leg of said E-shape, said armature is positioned in spaced relation to the ends of the legs of said E-shape and said gap is in a plane angular to the length of said spring means.

14. A system as set forth in claim 11 wherein said means for establishing said masses and spring means as a resonant system comprises .a plurality of electromagnetic means arranged radiallyxabout said spring means with each of said electromagnetic means comprising an arm-ature and stator With said armature rigidly connected to one mass and said stator to the other and forming a gap therebetween such that when said stator is energized said masses will move toward and away from one another at said resonant frequency.

15. A system for continuous Wet grinding material comprising container means formed of an elongated passage with a plurality of reverse bends interconnecting portions of said passage and with said portions lying primarily in parallel planes, said container means comprising a first mass, means for retaining grinding particles within said portions and for passing said material therethroug h, a second mass, spring means comprising -a plurality of parallel fiat members each having -a stiffness when loaded at the center and clamped at the edges determined by the formula where E=Youngs modulus in dynes/cmP, t=the thickness of the member in cms., and R=the effective radius of the member,

said members clamped together in pairs at their outer periphery with adjacent members of adjacent pairs connected together at their center, the outermost of said memhers connected at their centers one to said first mass and the other to said second mass, and means for establishing a resonant vibration in said system with said first mass moving at the resonant frequency of said system and with accelerations in excess of the acceleration of gravity.

16. A device as set forth in claim 15 wherein said means for establishing vibrations in said system includes a plurality of electromagnetic means having armatures and stators arranged radially about said spring means, means extending longitudinally of said spring means rigidly interengaging said armatures to one mass and said stators to the other mass, and means for exciting said electrom-agnet at a frequency equal to the resonant frequency of said system.

References Cited by the Examiner UNITED STATES PATENTS 264,344 9/82 Schmidt et al. 241l53 2,198,637 4/60 Smith 25972 2,534,123 12/50 H-asselhorn.

2,693,320 11/54 Smith 241-475 2,760,729 8/56 Mittag et al 241 X 2,904,729 9/59 Harwood 317-191 2,983,454 5/61 Podmore et al 241-175 X FOREIGN PATENTS 1,148,170 6/57 France.

I. SPENCER OVERHOLSER, Primary Examiner. ROBERT A. OLEARY, Examiner. 

1. A METHOD OF CONTINUOUSLY GRINDING MATERIAL COMPRISING, FEEDING MATERIAL CONTINUOUSLY IN A PATH HAVING PARALLEL SEGMENTS IN SERIES, SAID PARALLEL SEGMENTS BEING STATIONARY WITH RESPECT TO ONE ANOTHER, CONFINING GRINDING PARTICLES IN SAID PARALLEL SEGMENTS, AND VIBRATING SAID MATERIAL AND PARTICLES WHILE IN SAID SEGMENTS OF SAID PATHS AND IN A STRAIGHT LINE DIRECTION NORMAL TO THE AXIS OF SAID SEGMENTS AND WITH A FORCE SUBSTANTIALLY IN EXCESS OF THE FORCE OF GRAVITY.
 5. A SYSTEM FOR CONTINUOUS GRINDING OF MATERIAL COMPRISING, MEANS HAVING A MASS FOR CONTAINING SAID MATERIAL COMPRISING A PLUALITY OF ELONGATED CONTAINERS POSITIONED WITH THEIR LONGITUDINAL AXES PARALLEL TO ONE ANTOHER, MEANS INTERCONNECTING SAID CONTAINERS END TO END IN SERIES WHEREBY SAID MATERIAL MAY BE FED CONSECUTIVELY THROUGH SAID CONTAINERS, MEANS FOR VIBRATING SAID MASS IN AND MEANS FOR LIMITING MOVEMENT OF SAID MASS TO A STRAIGHT LINE DIRECTION NORMAL TO SAID AXIS WITH A RATE OF ACCELERATION IN EXCESS OF THE ACCELERATION OF GRAVITY. 